1. Field of the Invention
This invention relates to a device, system and method for slip forming reinforced concrete structures. More specifically, this invention is directed to a tunnel mold having at least one tunnel through the mold, to a slip molding system utilizing a tunnel mold and to the method for the slip forming a reinforced concrete structure having a reinforcing iron work array, (also “rebars”), wherein a portion of the iron work array is embedded in a slip formed concrete structure; and, a portion of the iron work array extends from within the slip formed, reinforced concrete structure. The portion of reinforcing iron work array, (rebars”) which extends from within the slip formed concrete structure, is and remains essentially concrete free concrete later integration into yet another slip formed structure. These extending reinforcing bars are suitable for subsequent reinforcement, and integration, with an additional in situ formed concrete structures, so as to further integrate such additional in situ formed concrete structures with the reinforced concrete road structures produced by this process. The concrete structures produced with a slip mold of this invention, are seamless, and formed in place, so as to better conform to the supporting surface on which they are formed.
2. Description of the Prior Art
Slip forming of concrete structures is a well-known technique for preparation of structural concrete elements for various industrial and public works (road, conduit, etc.) projects. Slip forming is a construction method in which a quick setting concrete is poured into the mold cavity of a slip-mold, and the slip-mold is progressively advanced or slipped over an iron work array composed of rebars, while the slip mold cavity of the progressively advanced over the iron work array. The rate of advancement of the mold, relative to the iron work array, is determined, in part, by the green strength of quick setting concrete in the formed concrete structure, specifically, the extent to which the concrete in the formed structure is self supporting, and is capable of supporting a forward advancing mass of unset concrete, as this advancing mass of concrete leaves the confines of the slip-mold.
Slip forming enables continuous, non-interrupted, cast-in-place “flawless”, (i.e. no joints), concrete structures which have superior performance characteristics to piecewise construction, using discretely formed elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated, (via vibration), yet quick-setting enough to emerge from the form with strength (also “self supporting strength” or “green strength”). This green strength is needed because the freshly set concrete must not only permit the form to “slip” upwards/forward, but also support the freshly poured concrete above it (“vertical slip forming”) and/or the freshly poured concrete in front of it (“horizontal slip forming”).
In vertical slip forming, the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip-form rises at a rate which permits the concrete to harden (develop green strength) by the time it emerges from the bottom of the form. In horizontal slip forming for pavement and traffic separation walls, concrete is laid down, vibrated, worked, and settled in place, while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.
The following is a representative (and not exhaustive) review of the prior art in this field:
U.S. Pat. No. 3,792,133 (to Goughnour issued Feb. 12, 1974) describes a method and an apparatus for concrete slip forming a highway barrier wall of varying transverse cross-sectional configuration for accommodating different grade levels on opposite sides of the wall, and wherein variations in the wall cross-sectional configuration may be readily accomplished during wall formation without requiring stopping, realignment or other interruptions in the screed movement during wall forming.
U.S. Pat. No. 4,266,917 (to Godbersen issued Mar. 12, 1981) describes a method for the efficient slip forming of highway median barrier walls of differing size (adjustable height) and shape having any arrangement of linear and curved sections and while the machine is being advanced in a single direction. The lateral adjustability of opposite side walls of the form, relative to the top wall, permits the use of the side walls with top walls of varying widths. The relative vertical adjustment of the top wall and side walls provides for a wide variation in the vertical height of a barrier wall particularly where a glare shield is to be formed on the barrier wall top surface. The slip forming of the glare shield takes place simultaneously and continuously with the slip forming of the barrier wall and over any selected portion of the wall while the machine is being advanced in a single direction. At any adjusted position of the slip form, the skirt member associated with each side wall is adjustable to prevent any flow of concrete from between the ground or highway surface and the form.
U.S. Pat. No. 4,084,928 (to Petersik issued Apr. 18, 1978) describes an improved barrier forming apparatus and method whereby a barrier is formed continuously over a surface, the barrier having continuous reinforcing rods extending the length of the barrier and having cage reinforced standard supports at predetermined intervals along the length of the barrier. The Petersik improved barrier forming assembly comprising a concrete forming member having a form cavity extending there through; a concrete passing member having a concrete delivery opening for passing concrete or the like to the form cavity; and a positioning assembly comprising a support shaft and a door member pivotally supported at a forward end of the concrete forming member, the barrier being extrudable continuously via the form cavity from a rearward end of the concrete forming member. The door member selectively is positionable to partially seal the form cavity at the forward end of the concrete forming member and has rod clearance channels through which the reinforcing rods pass through the door member into the form cavity when the door member is so positioned to seal the form cavity. The rod clearance channels permit the door member to pass the reinforcing rods to open the form cavity at the forward end of the concrete forming member to allow the free passage of the barrier forming assembly over the cage reinforced standard supports.
U.S. Pat. No. 5,290,492 (to Belarde, issued May 1, 1994) describes a system for continuously forming a concrete structure (a) having a predetermined cross-sectional configuration, (b) which extends along an elongate path, and (c) includes an outer surface having a textured pattern comprising concave or convex portions which extend other than just parallel to the elongate path. The system includes a frame, a first form assembly, a second form assembly, a drive system, and a support assembly.
As is evident from the above, there are number of alternatives for the slip forming of structures for use in road and bridge construction. The numerous alternative systems have their proponents and their detractors. In the context of selection of the more appropriate and efficient system, for example, for construction of retainer/barrier walls and/or glare shield concrete structures, time is money and often is reflected in the bidding process. More specifically, the bid letting on highway construction projects routinely include both penalty provisions for tardy completion and/or bonus payments for early completion. Accordingly, efficiencies which advance project completion, generally translate into cost saving. Thus, there is continuing efforts to automate, where possible, the fabrication of structural concrete components in highway construction; and, to standardize the process for the fabrication of roadway components and thereby simplify the bid letting on such projects, particularly federally funded highway construction projects.
Up to now, the standard or generally accepted techniques for the fabrication of bridge coping for an overpass on the highway, have required either the use of a pre-cast coping element (fabricated off-site), and/or the manual casting of a coping on-site, utilizing traditional forms and concrete casting techniques. In the case of a pre-cast concrete coping element, the road bed of the overpass requires special preparation since the pre-cast element does not readily conform to the angle of incline or grade of a ramp or overpass and, therefore, imperfectly abut one another upon placement on the incline of the bridge overpass. Accordingly, additional installation expense is required to insure the connection of abutting pre-cast copings to one another to insure the formation of a unitary coherent structure.
Alternatively, the on-site casting of an overpass/bridge coping, using the a manual process for forming the coping, specifically, traditional forms and concrete casting techniques, is preferably to the pre-cast coping, because the resulting coping is structurally continuous, and better conforms to the incline/grade of the ramp or overpass. Notwithstanding, the on-site casting of a bridge coping, by traditional concrete casting techniques, is very labor intensive and does not, without an inordinate amount of man power, lend itself to rapid fabrication and accelerated completion schedules. In each of the foregoing alternatives, the coping is formed with extending rebars for the later integration of the coping into a road bed pad and/or the attachment to a retaining wall, which can be later formed on the top of the coping.
Accordingly, there continues to exist the need for improved slip-mold design to both simplify the on-site fabrication of a bridge coping, minimize the manual labor requirements, permit/accommodate accelerated construction schedules, and yet produces a structure which is both coherent (e.g. monolithic structure), and faithfully conforms to the angle of incline or grade of a road overpass, without additional extensive on-site preparation.